The short answer
Most blockers hold back only plant iron, the kind in beans, grains, greens, eggs and iron tablets: coffee, tea and herbal teas, matcha, cocoa, red wine, phytates and oxalates. Calcium is the one that blocks iron from meat and fish too. None of them is a food to avoid: timing and the rest of the plate matter more.
| Blocker | Found in | Blocks | What to do |
|---|---|---|---|
| Polyphenols | Coffee, black and green tea, matcha, cocoa, red wine | Plant iron | Coffee and tea 1 h before or 2 h after, matcha 3–4 h |
| Herbal teas | Chamomile, linden, peppermint | Plant iron | Time them like tea |
| Calcium | Milk, yogurt, cheese, calcium supplements, tahini, almonds | Both kinds | 3–4 h from any iron |
| Phytates | Beans, lentils, whole grains, nuts, seeds, bran | Plant iron | Soak, sprout, ferment, add vitamin C |
| Oxalates | Spinach, chard, rhubarb | Plant iron | Add vitamin C, and count spinach as colour, not iron |
| Eggs | Egg white and whole eggs | Plant iron in the meal | Pair eggs with pepper, tomato or parsley |
- %79–94Less plant iron absorbed from a bread meal with black tea
- %50–60Less iron from a meal with 165 mg of calcium from milk or cheese
Four common mix-ups
- "Coffee blocks all iron." It holds back plant iron and iron tablets. Iron from meat and fish barely notices it.
- "Herbal tea is safe with meals." In one study chamomile and linden held back about half the plant iron in a meal, and peppermint as much as black tea.
- "Milk in tea softens it." Milk made little or no difference to the blocking, and it brings calcium, which blocks iron too.
- "Beans and whole grains are bad for iron." They are some of the best plant iron there is. Soaking, sprouting, sourdough and vitamin C get more of it in.
Timing beats giving things up
You don't need to give up coffee, tea or dairy. Give them their own time of day: coffee or tea 1 hour before or 2 hours after a plant-iron meal, matcha 3 to 4 hours, dairy 3 to 4 hours from any iron. Many people make breakfast their coffee and dairy meal, and put iron into lunch and dinner.
Iron tablets count as plant iron, so the same blockers apply. That is one reason the program takes iron at bedtime, far from the day's coffee and dairy.
More on each: coffee, tea, matcha and herbal teas, calcium. And the other half: how to absorb more iron.
Questions
Which blocker is the strongest?
Of the drinks measured, black tea and peppermint tea: 79–94% and 84% less plant iron from a bread meal. Calcium is the one that also blocks iron from meat and fish.
Do I have to give up dairy?
No. Give it its own meal or snack, 3 to 4 hours from iron. Butter has very little calcium, so cooking with it is fine.
Is rooibos a safe tea?
It looks like the mildest. In one small, older study rooibos made no clear difference to iron absorption, while ordinary tea cut it sharply.
Sources
- 1.Hurrell R.F., Reddy M., Cook J.D. Inhibition of non-haem iron absorption in man by polyphenolic-containing beverages. British Journal of Nutrition, 1999
- 2.Morck T.A., Lynch S.R., Cook J.D. Inhibition of food iron absorption by coffee. American Journal of Clinical Nutrition, 1983
- 3.Hallberg L. et al. Calcium: effect of different amounts on nonheme- and heme-iron absorption in humans. American Journal of Clinical Nutrition, 1991
- 4.Hallberg L., Brune M., Rossander L. Iron absorption in man: ascorbic acid and dose-dependent inhibition by phytate. American Journal of Clinical Nutrition, 1989
- 5.Hesseling P.B., Klopper J.F., van Heerden P.D. The effect of rooibos tea on iron absorption. South African Medical Journal, 1979
- 6.NIH Office of Dietary Supplements. Iron: fact sheet for health professionals
- 7.The Iron Guide, part 4: Food that counts
This page has not been reviewed by a clinician yet. Read it as general education, and take your own results to your doctor.
Educational, not medical advice. ferritin.ai does not diagnose or treat any condition, and it never sets a dose. Talk to your doctor about your own results.